In the July 8 edition of Science an interesting study is presented by Miller et al. (2005) and commented by Johnson (2005) on the impact of human activities. Around 45,000 years ago, the human started to occupy Australia, and like similar puzzles in the Americas, the questions is the impact of human activities on the extinction of many large herbivores. Miller et al. (2005) provide “the best evidence to date that human arrival, rather than climate, played the leading role in the extinctions of many large herbivores in Australia. They look especially to the diets of the emu and of the largest flightless but now extinct bird Genyornis.
Figure compares Genyornis & Emu.
The analysis of the changes in the diets point to major ecological changes that cannot be attributed to climate, which was relatively stable at this time. The results suggest that human arrival had a larger impact than the entire last glacial cycle on ecological change in Australia.
Gifford H. Miller, Marilyn L. Fogel, John W. Magee, Michael K. Gagan, Simon J. Clarke, and Beverly J. Johnson 2005. Ecosystem Collapse in Pleistocene Australia and a Human Role in Megafaunal Extinction, Science, Vol 309. Issue 5732: 287-290
Abstract of Miller et al 2005
Most of Australia’s largest mammals became extinct 50,000 to 45,000 years ago, shortly after humans colonized the continent. Without exceptional climate change at that time, a human cause is inferred, but a mechanism remains elusive. A 140,000-year record of dietary 13C documents a permanent reduction in food sources available to the Australian emu, beginning about the time of human colonization; a change replicated at three widely separated sites and in the marsupial wombat. We speculate that human firing of landscapes rapidly converted a drought-adapted mosaic of trees, shrubs, and nutritious grasslands to the modern fire-adapted desert scrub. Animals that could adapt survived; those that could not, became extinct.
Christopher N. Johnson 2005. The Remaking of Australia’s Ecology, Science, Vol 309, Issue 5732: 255-256